WO2008055456A1

WO2008055456A1 - Method and apparatus for determining the homogeneity of a mixture

Info

Publication number: WO2008055456A1
Application number: PCT/DE2007/001787
Authority: WO
Inventors: Tomas Qvarfort; Thomas Schneider
Original assignee: Tomas Qvarfort; Thomas Schneider
Priority date: 2006-11-07
Filing date: 2007-10-08
Publication date: 2008-05-15
Also published as: WO2008055456B1; US20100054077A1; DE102006052672A1; EP2089693A1

Abstract

Method and apparatus for determining the homogeneity (3) of a mixture. Known mixing methods require multiple calibration passes in order to automatically determine the end point of a mixing operation. This signifies a high level of complexity in the case of continuously changing products. The object of the present invention is to make it possible to automatically determine the end point of a mixing operation without having to carry out calibration passes. This is achieved by creating continuous spectral analyses of the mixture. As soon as the variance is under a tolerance (8) over a predefinable amount of time, the mixture is deemed to be homogeneous. The invention also relates to the determination of the end point of a mixing operation and to substance classification.

Description

METHOD AND DEVICE FOR DETERMINING THE HOMOGENITY OF A MIXTURE

The invention relates to a method and a device for determining the homogeneity of a mixture.

In industrial mixing processes, be it for the production of plastics, foods or medicines, increasingly higher demands are placed on the quality of the products to be produced. Mixtures must be precisely measured down to the last detail and thoroughly mixed before they can be passed on to the customer. A relatively easy-to-understand example of this is the production of instant soups, in which the use of an ingredient in too large an amount can mean a significant change in taste. Poor mixing of such a product can also lead to this result if, for example, due to the poor mixing in a sales unit, too large a proportion of salt is added which is correspondingly lacking in another sales unit.

This may be critical in the composition of medicaments where the addition of an active ingredient in a drug may cause a damaging rather than curative effect when it exceeds a limit of that agent. Ultimately, the quality of a product can not be guaranteed as far as its composition and mixing are unreliable.

For this reason, in the industry is increasingly going on, the operations of assembly and mixing and the Automate quality control. Spectral analyzes, for example using near-infrared spectrometers (NIR spectrometers), make it possible to determine the composition of a mixture quickly and accurately. This is conventionally effected by first acquiring a reference product by means of the spectrometer and thus creating a model spectrum with which the product to be mixed is compared in the later industrial process. In order to be able to take into account any deviations from an exact model spectrum, several runs of such reference measurements are usually carried out, in some cases up to 30 reference measurements for each product. This represents a huge effort, but without the traditional methods, a reliable determination of the product can not be done.

In the same way, it is tested according to conventional methods whether homogeneity of the mixture has already occurred, namely by determining a required proportion of predefined substances on the basis of reference measurements. The required mixing is achieved when, in a number of continuously performed measurements, the proportion of these substances reaches the respective reference value. However, this again creates new problems if a change in the recipe leads to a different concentration of the substance mentioned. If, during the preparation of the recipe for the mixture to be made, this particular ingredient should not be added for any reason, homogeneity will not be achieved in principle. Therefore, an end point of the mixing process can not be determined.

Against this background, the present invention, the object of a method and an apparatus for Determination of the homogeneity of a mixture of at least two substances or of a substance of different granularity, which precludes previous reference measurements for the classification of the mixed products and which, independently of the composition of a mixture, can determine its degree of homogeneity.

This object is achieved by a method according to the features of the main claim, as well as a device according to the features of the independent claim 11. Further useful embodiments of the method and the device are to be taken from the respective subclaims.

According to the invention, the homogeneity of a mixture of at least two substances or of a substance of different grain size is determined by performing a plurality of snapshots of the spectrum of the mixture during the mixing, preferably with the aid of an NIR spectrometer: The individual snapshots of the spectrum - Rums are compared and recorded the variation of the spectral curve over time. As soon as the variation of the spectrum over time falls below a limit value, which corresponds to the exceeding of a limit value of the homogeneity, the mixture is regarded as homogeneous. This has the advantage that, regardless of the composition of the mixture, the homogeneity of the currently present substance can be determined. This eliminates any upstream reference measurements, which would be costly and time-consuming to repeat in particular changes in the product to be produced. Also eliminates the problem that forgetting or for other reasons, the non-addition of a particular substance, an end point of the mixing process could not be detected. The process will in this way both simpler, as well as more cost effective and safer.

It may happen in the course of a mixing process that the mixture would have to be considered homogenous within a certain period of time. Such a homogeneity between several consecutively performed snapshots of the spectrum can be produced very easily by taking the aforementioned snapshots one after the other at very short intervals, so that a change in the too briefly selected intermediate time does not take place. Consequently, it makes sense to regard a mixture as homogeneous only when the variation of the spectrum moves within a tolerance range for a whole observation period. It is prevented in this way that within the mixing process by random processes, the impression of homogeneity is temporarily generated, while in fact is not yet complete homogeneity.

The very fact that uneven intermediate results can occur during the mixing process> makes it also useful to repeat the snapshots of the spectrum continuously.

As soon as the homogeneity of a mixture could be determined in a prescribed manner, a next step follows, in which the now homogeneous mixture is classified on the basis of previously stored model spectra. For this purpose, the model spectra are compared with the spectrum of the mixture in its end point, ie in the homogeneous state, and in the case of a match of the mixture with one of the model spectra, the mixture is classified according to specification of the relevant model spectrum. As far as a match with a On the other hand, it is possible to define the spectrum, which has not yet been classified, as a new model spectrum and thus to incorporate a new product definition into the system.

In order to be able to obtain a comparable sequence of each mixing process, it has proven to be useful to detect the beginning of a mixing process in such a way that the spectral analysis begins synchronously with the mixing process. In this case, the start of the mixing process is detected automatically, whereupon the spectral analysis is started. Analogously, once a tolerance limit of the degree of homogeneity and simultaneous coincidence of the detected spectrum with one of the model spectra has been exceeded, the mixing process is automatically terminated, with synchronization also advantageously taking place here.

In individual cases, it may of course also happen that a mixing process does not lead to a homogeneous substance, thus an endpoint even after this improved process is not achieved. In this case, a maximum period is provided after which the mixing process is stopped in any case, provided that during this time neither the desired homogeneity sets nor a match with a model spectrum is achieved.

Depending on the desired accuracy, each variable framework condition, such as the tolerance range of the homogeneity, the length of the observation period and / or the maximum duration of the mixing process can advantageously be set variably. For example, in the food industry a lower homogeneity of the product is tolerable than in the field of pharmacy. A device according to the invention for determining the homogeneity of a mixture of at least two substances or of a substance of different grain size is produced from a controllable mixing device, a spectrometer, preferably an NIR spectrometer, and from a data processing device. The Datenverarbeitungsgerat controls the entire mixing process, wherein after the start of the mixing process by starting the controllable mixing the spectral analysis is also started. The data resulting from the spectral analysis are fed to the data processing device and the comparison with the model spectra present in a database and a decision about the equality of the determined spectrum and model spectrum are made. Incidentally, the Datenverarbeitungsgerat has the conventional features and capabilities of a control system.

Samples can advantageously be removed from the device for further analysis, so that, if appropriate, the result of the device can be checked manually, or a result which has not yet been defined or classified can be fed to further analyzes.

The invention described above is explained in more detail below with reference to an exemplary embodiment schematically illustrated in the drawing.

Show it

Figure 1 is a graph of homogeneity in the course of a mixing operation, the degree of homogeneity over time is plotted, and FIG. 2 shows the snapshot of a spectrum in FIG

Frame of a mixing process, the shares are applied above the reflection frequency.

FIG. 1 shows a possible course of the homogeneity of a mixture over the mixing period. The diagram is in a coordinate system in which the time axis 2 is plotted as the transverse axis, the degree of the homogeneity 3 as the vertical axis. The mixing process is started synchronously at the beginning of a spectral analysis in a first time window 4, extends over two further time windows, to a fourth time window 5, within which the homogeneity of the mixture is achieved. The spectral analysis on which the homogeneity of the mixture is based is carried out with the aid of a near-infrared spectrometer (NIR spectrometer) and evaluated by means of a data processing device. The data processing device also controls a mixer, with which the mixing of the substances to be mixed or the different grains to be mixed is achieved.

First, the degree of homogeneity of the mixture in the first time window 4 is very low, which is due to the initially very low mixing of the substances or grains to be mixed. The homogeneity increases sharply as a result of the continuous mixing, reaches within the first time window 4, even for a short homogeneity phase 6, a tolerance range of the homogeneity which is sought for the mixture. This tolerance range is above a tolerance limit of 8, which is typically about 95% and in the present case in the course of the mixture, however, falls short again after a short time. Also in a second time window If this tolerance limit 8 is briefly exceeded again, however, there is no continuous improvement in the homogeneity, so that the mixing process is not interrupted at this point. Only in the fourth time window 5 the homogeneity continuously increases in the tolerance range between tolerance limit 8 and homogeneity upper limit 9, of which the latter represents a homogeneity of 100%. Only in this fourth time window 5 does the homogeneity remain in the tolerance range for a sufficient observation time, without, however, deviating negatively from it. Consequently, the system now considers the mixture homogeneous.

Mathematically, the homogeneity is calculated as described below. The spectrum X < _t , _π o can be determined by

- ^ - (/, »;) ~ ¹ {t, n) ^'r {ιι, m) ~ * ^~ ^ \ ι, m) where T are the eigenvalues of the line descriptions and P are the eigenvectors of the column descriptions. The value E is a remainder, which in special cases can also become zero. Homogeneity H _t then results

where the eigenvalues of the line descriptions depend on the time t.

FIG. 2 shows a possible spectrum 10 as a snapshot of a composition of the mixture to be considered. The graph shows on the vertical axis the portion 12 of the respective wavelengths of light which are reflected by the constituents of the mixture, over the said reflected wavelengths of light 11 as a longitudinal axis. This spectrum 10 is controlled by the spectrometer in the arrangement according to the invention. recorded continuously. Over time, so the mixing time away, the spectrum 10 changes depending on the momentarily detectable for the spectrometer substance. The variance of the spectrum is detected by the data processing device and converted into the homogeneity profile 1 previously considered in FIG. A very large variance corresponds to a very small homogeneity, and vice versa, a variance of almost zero corresponds to a homogeneity of almost 100%.

Simultaneously with the determination of the variance of a graph, it is compared with model spectra already stored in the memory of the data processing device, whereby a classification of the mixture is made. If the mixture corresponds to or even corresponds to a model spectrum during a period of consideration of the mixing process, the mixture is classified according to the model spectrum found by comparison.

Thus, the foregoing is a method and apparatus for determining the homogeneity of a mixture of at least two

Substances or about a substance of different grain size described, according to which a determination of the homogeneity without prior reference measurements is possible in that the

Spectrum of the mixture is continuously detected and based on the variance of the degree of homogeneity is determined.

Likewise, using model spectra, a comparison is made with already known mixtures, resulting in a

Classification of the currently produced mixture is possible. LIST OF REFERENCE NUMBERS

1 homogeneity course

2 timeline

3 degrees of homogeneity

4 First time window

5 Fourth time window

6 Short homogeneity phase

7 homogeneity area

8 tolerance limit

9 upper limit of homogeneity

10 spectrum

11 Reflected wavelength of light

12 share

Claims

PATENT APPLICATIONS

1. A method for determining the homogeneity of a mixture of at least two substances or about a substance of different grain size, wherein by means of a Spektrom- ters a plurality of snapshots of the spectrum (10) of the mixture created and in relation to at least one previous snapshot of the change is determined and, due to the variation of the spectrum (10), a degree of homogeneity is determined.

2. The method according to claim 1, characterized in that a mixture is considered homogeneous if the variation of the spectrum (10) for a period of observation ('4,5) runs exclusively within a tolerance range.

3. The method according to any one of claims 1 or 2, characterized in that the snapshots of the spectrum

(10) of the mixture are created continuously. Method according to one of the preceding claims, characterized in that after reaching a homogeneity in the tolerance range, the determined spectrum (10) of the mixture, preferably automatically, compared with pre-stored model spectra and in the case of a match the mixture is classified according to the matching model spectrum.

4. The method according to any one of the preceding claims, characterized in that after reaching a homogeneity in the tolerance range, the determined spectrum (10) of the mixture, preferably automatically, with pre-deposited model spectra are compared and in the case of a match, the mixture is classified according to the matching model spectrum.

5. The method according to any one of the preceding claims, characterized in that in the case of a mismatch of the spectrum (10) of the mixture with pre-stored model spectra recording of the spectrum (10) is made possible as a model spectrum.

6. The method according to any one of the preceding claims, characterized in that the spectrum (10) is formed by means of a near-infrared spectral analysis.

7. The method according to any one of the preceding claims, characterized in that the beginning of a mixing process is detected automatically, wherein the spectral analysis begins at least almost synchronously with the mixing process.

8. The method according to any one of the preceding claims, characterized in that after exceeding a tolerance limit (8) of the degree of homogeneity (3) and coincident with one of the model spectra, the mixing is automatically terminated, the spectral analysis at least almost synchronously with the mixing process ends.

9. The method according to any one of the preceding claims, characterized in that the mixing process after a maximum period within which exceeding the tolerance limit (8) of the degree of homogeneity does not take place and / or a match with a model spectrum is not achieved, is canceled.

10. The method according to any one of the preceding claims, characterized in that boundary conditions such as the tolerance range (8,9) of the homogeneity, the length of the observation period (4,5) and / or the maximum duration can be predetermined.

11. An apparatus for determining the homogeneity of a mixture of at least two substances or about a substance of different grains, comprising a controllable mixing device for mixing the substances, a spectrometer for creating a plurality of snapshots of the spectrum (10) of the mixture, and a data processing device for determining changes in the mixture with respect to at least one previous snapshot and for determining a degree of homogeneity of the mixture due to the variation of the spectrum (10) and for controlling the mixing plant.

12. The device according to claim 11, characterized in that a near-infrared spectrometer (NIR spectrometer) is used as the spectrometer.

13. Device according to one of claims 11 or 12, characterized in that the mixture samples for further analysis, preferably automatically, are removable.

14. The device according to one of claims 11 to 13, characterized in that an evaluation of the determined spectra (10) by means of the data processing device is automatically carried out.